This invention relates to a process for purifying halogenated aromatic sulfone or ketone compounds. In a specific aspect, the invention relates to a process for purifying 4,4'-bis(p-chlorophenylsulfonyl)biphenyl.
Halogenated aromatic sulfone or ketone compounds can be produced by the Lewis acid catalyzed condensation of an aromatic hydrocarbon with a halogenated aromatic containing the sulfone or ketone group. For example, 4,4'-bis(p-chlorophenylsulfonyl)biphenyl can be produced by reacting 4-chlorobenzenesulfonyl chloride with biphenyl using nitrobenzene as a solvent in the presence of a Lewis acid catalyst such as ferric chloride or aluminum chloride. The crude 4,4'-bis(p-chlorophenylsulfonyl)biphenyl reaction mixture contains unreacted 4-chlorobenzenesulfonyl chloride, bis(chlorophenyl)sulfone which is an impurity in the 4-chlorobenzenesulfonyl chloride, and 4-(4-chlorophenylsulfonyl)biphenyl which is the mono-halo substituted product.
Purification of applicable halogenated aromatic sulfone or ketone compounds has been a problem due to low solubility in most organic solvents and the very similar or higher solubility of undesirable mono-halo substituted reaction products. For example, when the halogenated aromatic sulfone or ketone compounds are used as monomers for arylene sulfide polymers, these side products must be removed because they act as chain terminators during the polymerization.
Typical recrystallization processes can produce high purity halogenated aromatic sulfone or ketone compounds, but they have the disadvantages of low throughput, difficulty in removing residual solvent, and difficulty in scaling to pilot plant or commercial operations. A purification process which is economical, commercially viable, and can utilize inexpensive solvents to produce high purity product with good yield is highly desirable.